Merge pull request #27508 from abhishek-gola:if_layer_add

IfLayer add to new DNN engine #27508

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/src/init.cpp

@@ -84,6 +84,7 @@ void initializeLayerFactory()
     static ProtobufShutdown protobufShutdown; CV_UNUSED(protobufShutdown);
 #endif
 
+    CV_DNN_REGISTER_LAYER_CLASS(If,             IfLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Concat,         ConcatLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Concat2,        Concat2Layer);
     CV_DNN_REGISTER_LAYER_CLASS(ConstantOfShape, ConstantOfShapeLayer);